1. Field of the Invention
The present invention relates to negative active materials for rechargeable lithium batteries and rechargeable lithium batteries including the same.
2. Description of the Related Art
Rechargeable lithium batteries use materials that are capable of reversibly intercalating or deintercalating lithium ions as the positive and negative electrodes. Organic electrolyte solutions or polymer electrolytes may be used between the positive and negative electrodes. Rechargeable lithium batteries generate electrical energy by oxidation/reduction reactions occurring during intercalation/deintercalation of lithium ions at the positive and negative electrodes.
As positive active materials, chalcogenide compounds have been widely used. Composite metal oxides such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCOxO2 (0<x<1), LiMnO2, and so on, have also been used.
Conventionally, lithium metals have been used as negative active materials for rechargeable lithium batteries. However, when using lithium metal, dendrites can form which can cause short circuits, which, in turn, can cause explosions. Therefore, carbonaceous materials, such as amorphous carbon and crystalline carbon, have recently been used as negative active materials in place of lithium metals. However, such carbonaceous materials impart capacity losses of from 5 to 30% during the first several cycles, which wastes lithium ions and prevents at least one active material from being fully charged and discharged. Therefore, carbonaceous negative active materials have poor energy densities.
In addition, recent research has shown that metal negative active materials such as Si, Sn, and so on, which supposedly have high capacities, impart irreversible capacity characteristics. Further, tin oxide is an alternative to carbonaceous negative active materials. However, as the metal negative active material is included at 30% or less, initial Coulomb efficiency is decreased. Further, as lithium is continuously intercalated and deintercalated to generate a lithium-metal alloy, the capacity is remarkably decreased and the capacity retention rate is remarkably deteriorated after 150 charge and discharge cycles, making it not commercially viable.